Apparatus for controlling the feeding of paper in high-speed printers

ABSTRACT

Apparatus for controlling the paper feeding in printing apparatus, wherein the feed motor speed is controlled by the combined effect of a speed-space detector whose output is speedproportional voltage and said pulses are compared with a predetermined pulse number, and wherein the results of said comparison are employed in combination to provide a suitable paper feed power control through a bidirectional amplifier which does not require a stabilized power supply.

United States Patent 1 1 Bonzano 1111 3,740,634 June 19, 1973 1 1APPARATUS FOR CONTROLLING THE I FEEDING OF PAPER IN HIGH-SPEED PRINTERS[75] Inventor:

[73] Assignee: Honeywell Information Systems Italia S.p.A., Milan, ItalyGiorgio Bonzano, Caluso, Italy [62] Division of Ser. No. 54,815, July14, 1970, Pat. No.

3,450,973 6/1969 Tobey 318/345 3,523,228 8/1970 Currie 318/681 3,599,0638/1971 Nanai 318/327 Primary ExaminerBernard A. Gilheany AssistantExaminer-Thomas Langer Attorney-George V. Eltgroth, Lewis P. Elbingerand Aubrey C. Brine [57] ABSTRACT Apparatus for controlling the paperfeeding in printing 3,656,041 apparatus, wherein the feed motor speed iscontrolled 52 US. Cl. 318/345 318/681 by f effect of Speed-Spacedetector 51 1111.11 "1102;, 5/16 whse speedfpmpomonal "P s and Said [58]Field of Search 318/327 345 331 Pulses are P predtermmed Pulse 3 8 her,and wherem the results of sa1d comparison are employed in combination toprovide a suitable paper feed [56] References Cited power controlthrough a bidirectional amplifier which UNITED STATES PATENTS does notrequ1re a stabllized power supply.

3,538,353 11/1970 Hanger 318/345 2 Claims, 8 Drawing Figures PatentedJune 19, 1973 5 Sheets-Sheet 1 MPLIFIER VOLTAGE COMPARATOR REFERENCEVOLTAGE LOGIC DEVICE\ .21, w

GENERATOR Patented June 19, 1973 5 Sheets-Sheet 3 m QE ll l.l.l l|||IIIL Patented June 19, 1973 5 Sheets-Sheet 4 EMM Patented June 19, 19735 Sheets-Sheet 5 APPARATUS FOR CONTROLLING THE FEEDING OF PAPER INHIGH-SPEED PRINTERS This is a division, of application Ser. No. 54,815,filed July l4, 1970, now U.S. Pat. No. 3,656,041.

BACKGROUND OF THE INVENTION This invention relates to apparatus forcontrolling the paper feeding in high-speed printers, particularly inprinters employed in information processing systems. Accordingly, thisinvention concerns apparatus for controlling the acceleration, thebraking, and-the reversal of a low inertia motor according to apredetermined sequence.

The feeding of paper in high-speed printers is usually provided by meansof a motor which drives a system of sprocket, or toothed, wheels orchains, whose teeth engage in a set of sprocket holes provided in thepaper. The distance of the paper advancement must be an in tegralmultiple of a definite quantity, usually the minimum spacing betweenconsecutive printed lines. This quantity is called the line pitch."

According to requirements, the paper may be controlled to advance, inresponse to an appropriate line feed signal, one, two, or even threeline pitches at a time during normal printing operations, to obtainprinted texts of different densities. The paper may also be controlledto advance through a large number of line pitches by the slew"operation, in which a substantially large portion of blank space isinterposed be tween portions of printed text.

Apparatus is known for precisely controlling the position of the paperat the end of each line feed or slew such pin-and-ratchet devices,gears, and the like. However,.devices are costly and are subject toconsiderable operation. This usually comprises mechanical means,

wear and tear as a consequence of the mechanical stresses to which theyare subjected. Moreover, they are usually noisy and frequently go out ofadjustment.

Other feed control apparatus uses low inertia motors for directlycontrolling the paper feed operation. Such motors may be, for example,direct current motors with printed-circuit rotors, controlled bybidirectional am .plifiers suitable for imparting to the motor highaccelerating or decelerating torques. The paper feed operation requires,in this instance, three states: a first state of fast acceleration, asecond state of constant speed, and

a third stateof fast deceleration (braking). In the first state thecontrolling amplifier delivers a large current of predeterminedpolarity. in the'second state .the cur-- rent delivered is only thatrequired to compensate for the energy lost by friction in order tomaintain the motor at constant speed, and in the third state theamplifier delivers a large current of reversed polarity. To

obtain the same distance of line pitch in each state, the motor speedand, therefore, the amplifier current deliv- Therefore, it is the objectof the instant invention to provide a paper feed control system of lowcost, great accuracy and high reliability.

SUMMARY OF THE INVENTION According to the invention this object isattained by supplying the motor from a bidirectional amplifier which iscontrolled by a signal provided from comparing a reference voltage and avoltage generated by a tachometric generator driven by the motor.Stabilization of the current delivered by the amplifier is obtained in asimple and efficient manner by stabilizing an intermediate stage of theamplifier utilizing low power 'Zener diodes.

Although the invention is primarily directed toward paper feeding in ahigh-speed printer, it may be used in a number of other instanceswherein it is necessary to control acceleration, constant speed, anddeceleration and reversal a rotating mechanical device driven by alow-inertia motor. For example, the invention is useful with the tapetransport capstan of a tape handler of the single capstan type.

BRIEF DESCRIPTION OF THE DRAWING,

' FIG. 4 is a schematic diagram of the bidirectional amplifier of FIG.1; and

FIG. 5 is a schematic diagram of a variation of the amplifier of FIG. 4;

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, a paperfeed motor 1 drives a toothed chain member 2. Member 2 engages sprocketholes in and thereby moves a paper web 3. Either shaft of motor 1, or onanother shaft directly driven by the motor, are mounted a photodisc 4,and a tachometric d-c generator '7. Disc 4 is provided at its peripherywith a set of uniformly spaced holes associated with a photoelectricpick-up device which comprises a lamp 5 and a photocell, or photodiode,6. Generator 7 delivers at its terminals a voltage proportional to theortational speed of motor 1.

The distance between adjacent holes on the periphery of photodisc 4corresponds to the angle through which motor 1 must rotate to advancepaper web 3 by a single line pitch. Therefore, photocell 6 receives alight pulse, and delivers an electric pulse, each time that the paperweb advances a line pitch.

The paper feeding occurs either step-by-step, each step spanning one,two or three line pitches, or by slewing," wherein the paper webadvances through a substantially larger number of line pitches. Althoughslewing may occur at different speeds, depending on amount of spacingrequired, the slew speed is always greater than the step-by-step speed.For example, three speeds may be employed: a low speed for thestep-bystep advancement, an intermediate speed for slow slewing,,and ahigh speed one for fast slewing. Possible values for these three speedsmay be 600 mm/sec., l,000 mm/sec., and 1,800 mm/sec.

In FIG. 1, a logical device 8 receives, instruction signals on an inputlead 9. The instruction signals correspond to the required type offeeding; i.e., step-by-step feeding by one, two or three line pitches,slow slew or fast slew, and number of pitches per slew operation. Thepulses delivered by photocell 6 are supplied to logical device 8 on aninput lead 10.

Logical device 8 responds to the instruction signals to control areference voltage generator 11, which generates a reference voltage Vfor determining the rotational speed of motor 1. The reference voltagegenerated by generator 11 is applied to an input lead 12 of a comparatorl3. Comparator l3 compares two voltages, reference voltage V and avoltage V termed the tachometric voltage. The tachometric voltage Vwhich is proportional to the voltage generated by tachometric generator7, is applied to input lead 14. The ratio between the tachometricvoltage V and the voltage delivered by generator 7 is so chosen, thatfor each different reference voltage, the tachometric voltage providedat the corresponding motor speed is .slightly lower than voltage VAssume, first, that this ratio is equal to unity, wherein voltage V isthe same as the actual voltage delivered by generator 7. In comparator13, the tachometric voltage is subtracted from the reference voltage.The difference voltage delivered by comparator 13 is a control voltage Vwhich is applied to an input lead 15 of a bidirectional amplifier 16.This difference voltage may be positive, if the reference voltage ishigher than the tachometric voltage, in which case the output lead 17 ofamplifier 16 delivers a positive control current which causes motor 1 torotate in a direction appropriate for feeding the paper. If thedifference-voltage is negative, amplifier 16 supplies to the motor anegative control current, which has a braking effect. If the differenceis zero, the motor is not supplied with control current.

The waveforms of FIG. 2 illustrate the reciprocal relationshipbetween'the tachometric voltage V and the control voltage V; andillustrate the current delivered to the motor, for the example of a fastslewing. In this example, respondingto the received instruction signals,logical device 8 selects a reference voltage representing the fast slew.Line R (waveform a) represents this reference voltage V and line Trepresents the corresponding tachometric voltage V Initially, when motor1 is at rest, the tachometric voltage is zero, so that the controlvoltage V ,'which is the difference between voltages V and V and isrepresented by line S (waveform b), is equal to reference voltage VAccordingly, amplifier 16 delivers a positive control current I, asshown by line I (waveform c).

As the motor starts turning and increases its speed,

the tachometric generator delivers an increasing voltage as representedby line T. The control voltage V correspondingly decreases, as shown byline S, which is the difference between the ordinates of lines R and T.When voltage V,- becomes less than a predetermined threshold value W,corresponding to the saturation conditions of. amplifier 16, the controlcurrent output I, decreases from its initial maximum value I and,therefore, the acceleration and the slope of curve T decrease. When thecontrol current is only sufficient to compensate for frictional. losses,the acceleration becomes zero and the motor runs at constant speed.

During the rotation of motor 1, the pick-up device associated withphotodisc 4 transmits a number of pulses, equal to the number of linepitches advanced, to logical device 8. Logical device 8 counts thesepulses by means of a counter. When thenumber of pulses received bydevice 8 reaches a quantity n-k, wherein n is the programmed number ofline pitches of the current slew, and k is an integer suitably chosen,for example 5, reference voltage V is reduced to the value V,,,corresponding to step-by-step feeding. Accordingly, V

becomes lower than V,-, and a negative control voltage V is delivered toamplifier 16, which thereupon delivers a negative control current I Thisnegative control current abruptly slows motor 1 and reduces its speed tothe step-by-step value.

This braking action requires, the duration of k photodisc pulses. Whenthe n"' pulse is received by logical device 8 the reference voltage isreduced to zero, the control voltage V again goes negative, and thebraking current brings the motor to a halt.

It is apparent that the precision of the final position reached by thepaper web at the end of a feeding operation is conditioned by theprecision of action controlled by thebraking current. If such action istoo strong, the paper'web halts too early, whereas if it is too weak,the paper overshoots the intended final position.

Reference voltage generator II, FIG. 3, comprises three transistor T,, Tand T for example of the NPN type. The collectors of these transistorsare supplied from a common positive voltage source, +V, (for example,+20 v) through respective resistors R,, R R The emitters of transistorsT,, T and T are grounded. The collectors of transistors T,, T and T arealso connected to the anodes of the respective diodes D,, D and D Thecathodes of these three diodes are all connectedto one end 25 of apotentiometer R,, whose other end is grounded. The bases of transistorsT,, T and T are connected to the respective input terminals 21, 22, 23.Terminals 21, 22, and 23 receive control signals from logical device 8,which correspond to the required referencevoltage to be delivered. Thecontrol signals on terminals 21, 22, and 23 represent binary values, thebinary I being represented by a positive voltage (for example instance+5V), and the binary 0 being represented by 0v.

When a binary 1 signal; i.e., a positive voltage, is applied to all ofthe three input terminals 21, 22, 23, the three transistors T,, T and Tconduct, their collector voltages drop practically to 0v, and,consequently, point 25 drops to 0v. Accordingly, reference voltage V,,on lead 12 is at 0v. In this instance, motor 1 is supplied with nocurrent and no paper feeding occurs.

If a binary 0 signal is applied to input terminal 21, while inputterminals 22 and 23 receive binary 1 signals, transistor T, becomesnonconductive. Current flows through resistor R,, diode D, andpotentiometer R,. Accordingly, lead 12 is brought to a reference voltageV, which depends on the values of resistor R, and potentiometer R andthe position of the movable tap of potentiometer R Since the resistanceof resistor R, is considerably greater than that of potentiometer R,,the reference voltage V, is substantially less than the source voltage,+V,. By adjusting the movable tap of potentiometer R,,, the value ofvoltage V, is brought to that required for step-by-step feeding.

If a binary 0 signal is applied to both input terminals 21 and 22,transistors T and T become nonconductive. Resistors R and R effectivelybecome parallel connected through respective diodes D and D Theresulting resistance value is lower than in the immediately precedingcase, so that the reference voltage at lead 12 is higher, being areference voltage V required for the slow slew.

If a binary 0 is applied to both input terminals 21 and 23, resistors Rand R become effectively parallel connected. Since the value of resistorR is relatively small with respect to that of resistor R the resultingresistance value is further reduced. Therefore the voltage at lead 12 isrelatively high, being the reference voltage V required for the fastslew.

The following table gives the binary values applied to the inputterminals for each of the four control conditions, and the relatedreference voltages provided:

Condition Input Terminals Ref. Voltage No feeding I l l O Step-by-step 0I I V,

Slow slew 0 0 v l V,

Fast slew 0- I 0 V Only four of the eight possible combinations ofbinary values at the three input terminals are used herein. Therefore,four remaining combinations are available if additional referencevoltages are needed. The choice of the four combinations is onlyrepresentative; different combinations may be selected depending on theresistance values and disposition employed. Moreover, since only fourreference voltages are employed in the preferred embodiment, only twoinput terminalsare required to provide the four different combinationsof applied binary values. However, such an arrangement might set toorigid a constraint on the voltage values obtainable from particularresistance values. .Instead, with the disclosed arrangement the valuesof the three resistances may be freely chosen to obtain the mostsuitable ratio between the three required feeding speeds.

The movable tap of potentiometer R, permits adjusting the step-by-stepfeeding speed to the required value. If R represents the portion ofpotentiometer R between the movable tap and ground, the'referencevoltage V is proportional to R. However, the ratios between the'variousreference voltages are independent of R, depending only on R,, R R and RThus,

adjusting the potentiometer tap does not change the ratios between thespeeds. I

A set of suitable values for these resistances is, for example, thefollowing:

ratios between reference voltages and corresponding I speeds are:

V /V 1.69 Vii/V 3.24

If the step-by-step feeding speed is, for example, 22 inches per second(560 mm/s) the slow slew speed is appr. 37 /2 inches per second (950mm/s) and the fast slew speed is 71 inches per second (1,800 mm/s).

Comparator 13, FIG. 3 comprises resistors R R and R connected as shown.The comparator receives the. reference voltage V on lead 12 and deliversthe control voltage V on lead 15, which is the input to amplitier 16,represented in FIG. 3 by its input resistance R The tachometricgenerator 7 is connected across leads 14 and 15 and delivers a voltage Vproportional to the rotational speed of motor 1, and, accordingly, tothe feed rate of the paper web. Resistors R and R form a voltage dividerso that between lead 15 and point 18 there is a tachometric voltage Vequal to: V' R (R R The resistance values R and R are chosen such thatthe tachometric voltage V is comparable to the reference voltage V i.e.,for each different reference voltage V there is a rotational speed ofthe tachometric generator for which V is equal to V Applying Theveninstheorem of electric circuits to the circuit comprising the tachometricgenerator and resistors R and R there is derived an equivalent circuitcomprising an ideal voltage generator G delivering voltage V in serieswith a resistor R whose resistance is that of resistors R and R inparallel;

ea e r/ 0 1) Accordingly, the equivalent circuit of comparator 13 isshown in FIG. 3a, where in G is an ideal voltage generator providing thereference voltage V and R' is a resistance equal to the sum of theresistances of resistor R and the portion R of potentiometer R, includedin the circuit P. The control voltage V is the voltage developed acrossresistance R The current I in the equivalent circuit of FIG. 3a

. is given by:

V V =(R R' R I Since V R 1, the equation may be written as:

:where K is a constant and V,- is a fictitious signal voltage V andvoltage V, is proportional to voltage V,.

This requires only changing the scale of waveforms a and b. Moreover,for V =V V,=0, and

I The bidirectional amplifier 16 of FIG. 4 provides the controlcurrentto motor 1. Amplifier 16 comprises a voltage preamplifierincluding two differential amplifiers and a final stage, which includetransistors T T T T and T and a current amplifier including a firststage which uses complementary transistors T and T,,,, a second stagewhich uses non-complementary transistors T and T and a final stage whichuses two parallel-connected power transistors T and T for the positiveoutput and two parallel-connected power transistors T and T for thenegative output.

The first differential amplifier comprises the NPN transistors T and TThe collectors of transistors T and T are supplied from the stabilizedvoltage source VA, through the respective resistor R and variableresistor R The emitters of transistors T and T are connected to thecollector of .a transistor T whose emitter is connected, in turn,through a resistor R to the stabilized negative voltage source VA. Thestabilized voltage sources +VA and VA are obtained respectively from twonon-stabilized supply voltages +V and V, applied to the respectivesupply terminals 33 and 34. These two supply voltages are substantially'equal in amplitude and are symmetrically connected with respect to areference voltage, which usually is the ground voltage.

Stabilization of the voltages +VA and VA is provided by stabilizingcircuits comprising the respective Zener diodes Z and Z resistor R and Rarranged according to well-known techniques.

A Zener diode Z is connected between the emitter of transistor T and oneend of resistor R thereby maintaining, in cooperation with resistor Rthe base of transistor T at a constant voltage with respect to thestabilized negative voltage VA. Thus, the current flowing throughresistor R is maintained at a constant value and, consequently, the sumof the currents flowing through transistors T and T is held constant.

The base of transistor T is connected through a resistor R to input lead15, on which the control voltage V is supplied. The base of transistor Tis connected to a point 35. Point 35 is the central pointof a voltagedivider comprising resistors R and R one end of such voltage dividerbeing grounded and the other end being connected to a terminal 17, whichsupplies motor 1. As it-will be explained hereafter, a feed-back effectis thereby obtained.

- When motor 1 is at rest, and no current flows therethrough, bothterminal 17 and point 35 are at ground voltage (v). If input lead 15 isalso at 0v., the same amount of current must flow through transistors Tand T Therefore, if R is equal to R' the collectors of transistors T andT are at the same voltage. This balanced condition can be achieved by afine adjustment of variable resistor R if it is necessary to compensatefor differences in the intrinsic resistance of the transistor. However,such differences usually will be very small,inasmuch as transistors Tand T are matched to have equal characteristics, to the extent possible.

The collector voltages of transistors T and T are applied to therespective bases of PNP transistors T and T which form the seconddifferential amplifier. The emitters of transistors T are connectedtogether and to one terminal of a resistor R which is supplied at itsother terminal from the positive stabilized voltage source =VA. Thecollector of transistor T is grounded. The collector of transistor T isconnected, through a resistor R to the negative stabilized voltagesource VA. This second differential amplifier is symmetrically driven bythe output signals of the first differential amplifier. The employmentof transistors -of opposite conductivity type for the first and seconddifferential amplifiers substantially reduces, through thiscompensation, the effect of temperature drift.

The collector of transistor T 5, is also connected to the base oftransistor T The emitter of transistor T is connected to the stabilizednegative voltage source VA. The collector of transistor T is suppliedform the stabilized positive voltagesource +VA through a resistor R anda diode D.

The amplifier comprising transistor T is the final stage of the voltagepreamplifier and is provided with output points 36 and 37, which differin voltage by the drop through diode D. In the quiescent condition;i.e., in the absence of an input control voltage V the voltages atpoints 36 and 37 are balanced with respect to the ground. In thisbalanced condition the voltage at point 36 is slightly positive and thevoltageat point 37 is slightly negative.

When a positive control voltage is applied to input lead 15, theconduction of transistor T increases and correspondently the currentflowing through transistor T decreases. The voltage of the collector oftransistor T and of the base of transistor T decreases, and the voltageof the collector of transistor T and of the base of transistor Tincreases. The resistance. of transistor T and, therefore, the voltagedrop between its emitter and collector increases, whereby the voltage ofthe base of transistor T decreases. Therefore, current flowing throughtransistor T decreases, whereupon the voltages of points 36 and 37increase. Conversely, when anegative control voltage is applied to inputlead 15, the voltages of points 36 and 37 decrease. HOwever, thedifference between the voltages of points 36 and 37, being equal to thedrop across diode D, does not change appreciably. 1

The above-described voltage preamplifier is followed by a currentamplifier. The first stage of this current amplifier comprises a pair ofcomplementary transistors T and T transistor T being, for example, ofthe NPN type,- and transistor T being of the PNP type. The collector oftransistor T is connected to the positive stabilized voltage source =VAthrough a resistor R and its emitter is connected to a point 38. Thecollector of transistor T is connected directly to the negativestabilized voltage source -VA, and its emitter is connected to point 38through a resistor R The voltages of points 36 and 37 are applied to thebases of respective transistors T and T In the absence of an inputcontrol voltage V both of transistors T and T are in a state of lowconduction; i.e., both are close to cutoff. When a positive controlvoltage is applied to input lead 15 both points 36 and 37 changepositively, as described previously herein. Because transistors T and Tare of opposite conductivity types, transistor T becomes more conductiveand transistor T becomes less conductive.

The collector of transistor T is connected to the base of transistor TThe emitter of transistor T is connected to the base of transistor TTransistors T and T are of the PNP type and, with resistors R R R and Rform an amplifier wherein each transistor is connected as an emitterfollower. Such amplifier provides a substantial amplification of theoutput current.

Transistors T and T drive respectively a pair of transistors T and T 0and a pair of transistors T and T Each of transistors T T T and T withrespective sets of resistors R R R R R R R R R and R R R 8 forms anemitter follower circuit The emitter follower comprising transistor T isin parallel with the emitter follower comprising transistor T both suchemitter followers being supplied by the positive supply voltage =V. Theemitter follower transistor T is in parallel with the emitter followercomprising transistor T both such emitter followers being supplied bythe negative supply voltage --V. In absence of an input control voltageV each of transistors T T T 21 and T is in a state of low conduction,being close to cutoff, so that only a relatively small current flows 35,the base of transistor T Thus, the difference between the currentsthrough transistor T and T decreases. Thus, a negative feed-back effectis provided, with its well-known advantages of greater stability andless sensitivity to noise.

The increase in conduction of transistor T and the decrease inconduction of transistor T cause a respective decrease of the basevoltage of transistor T and increase of the base voltage of transistor TThus, transistor T becomes more conductive and transistor T lessconductive. Under these conditions, the decreased voltage of the emitterof transistor T causes the conduction of transistors T and T toincrease, whereas the increased voltage of the emitter of transistor Tcauses the conduction of transistors T and T todecrease. Transistors Tand T thereby deliver a greater positive current and transistors T and Ta lesser negative current to terminal 17.

As a consequence, for a positive control voltage the motor connected toterminal 17 receives a positive cur- -rent and is accelerated asrequired. In the opposite case; i.e., wherein a negative control voltageis applied to lead 15, a negative current is supplied to the motor, withits consequent braking effect.

Since terminal 17 is directly connected to point 38, there is no need tostabilize the supply voltage in the current amplification stages whichfollow complementary transistors T and T,,,. In fact, the stabilizationof the voltage at points 31 and 32, ensures that the voltage of point 38is affected only by the control voltage at input lead 15 and not by.accidental fluctuation of the supply voltages +V and V.

Accordingly, the possible fluctuations of the nonstabilized voltagesupplying the following stages cannot influence the voltage of point 17,which supplies motor 1. Since the current required for the stage withthe complementary transistors T and T and the preceding stages issubstantially lower than that required for the'following power stages, aremarkable saving in cost and dimensions of the components of thestabilizing circuit is attained, relative to that which would berequired for stabilizing the voltages +V and V provided at terminals 33and 34.

A satisfactory result, with even a lower cost of the stabilizingcomponents, may be provided by the arrangement illustrated in FIG. 5.The circuit of FIG. 5 differs from that of FIG. 4 in that the supplyvoltage for the complementary transistors T and T is also notstabilized, but only the supply voltage for the preceding stages. Bythis arrangement, the stabilized voltages +VA and VA, obtained by use ofresistors R and R and Zener diodes Z, and Z are present at points 40 and41, whereas at points 31 and 32 the non-stabilized voltages +V and -Vare present.

I The current to be stabilized is further reduced and an additionalsaving thus results. In this instance the voltages of points 36 and 37,and therefore the voltages applied to the bases of transistors T and Tare independent of fluctuations of voltages +V and V. The effect of suchfluctuations on the voltage of point 38, however, although theoreticallynot zero, is effectively negligible. In fact,'this effect is reduced tothe changes in voltage drop across the base-emitter junctions oftransistors T and T due to changes in the current flowing through thesejunctions as a result of such voltage fluctuations.

I claim:

1. A bidirectional amplifier provided with an input terminal directlyconnected to the output terminal of a voltage comparator, comprising abidirectional voltage preamplifier fed by first and second stabilizedvoltage sources, said first and second voltage sources having equalamplitudes and opposite polarities with respect to a ground referencevoltage, a bidirectional current amplifier driven by said voltagepreamplifier through first and second connecting terminals, wherein afirst stage of said bidirectional current amplifier comprises a firsttransistor of NPN type having the collector thereof connectedto apositive supply voltage through a first resistor and the emitter thereofconnected to an output terminal and a second transistor of PNP type saidfirst transistor being connected to the base of a third transistorconnected in a first emitter follower circuit, said first emitterfollower circuit being connected between said positive supply voltageand said output terminal, the emitter of said second transistor beingconnected to the base of a fourth transistor connected .in a secondemitter follower circuit, said second emitter follower circuit beingconnected between said output terminal and said negative supply voltage,said first and said second emitterfollower circuits each driving atleast one a power emitter follower circuit. said power emitter followercircuits being symmetrically connected between said positive andnegative supply voltages and said output terminal; said output terminalbeing directly connected to one input terminal of said low-inertiamotor, a second input terminal of said lowinertia motor being connectedto said ground reference voltage. v

2. The bidirectional amplifier of claim 1 wherein the supply voltage ofsaid first stage of said current amplifier is not stabilized.

1. A bidirectional amplifier provided with an input terminal directlyconnected to the output terminal of a voltage comparator, comprising abidirectional voltage preamplifier fed by first and second stabilizedvoltage sources, said first and second voltage sources having equalamplitudes and opposite polarities with respect to a ground referencevoltage, a bidirectional current amplifier driven by said voltagepreamplifier through first and second connecting terminals, wherein afirst stage of said bidirectional current amplifier comprises a firsttransistor of NPN type having the collector thereof connected to apositive supply voltage through a first resistor and the emitter thereofconnected to an output terminal and a second transistor of PNP typehaving the emitter thereof connected to said output terminal through asecond resistor, and the collector thereof connected to a negativesupply voltage, said positive and negative supply voltages havingsubstantially equal amplitudes with respect to said ground referencevoltage; the base of said first transistor being connected to said firstconnecting terminal of said preamplifier and the base of the secondtransistor being connected to said second connecting terminal of saidpreamplifier, a diode suitably connected across said connectingterminals to provide a substantially constant voltage differencetherebetween; the collector of said first transistor being connected tothe base of a third transistor connected in a first emitter followercircuit, said first emitter follower circuit being connected betweensaid positive supply voltage and said output terminal, the emitter ofsaid second transistor being connected to the base of a fourthtransistor connected in a second emitter follower circuit, said secondemitter follower circuit being connected between said output terminaland said negative supply voltage, said first and said secondemitterfollower circuits each driving at least one a power emitterfollower circuit. said power emitter follower circuits beingsymmetrically connected between said positive and negative supplyvoltages and said output terminal; said output terminal being directlyconnected to one input terminal of said lowinertia motor, a second inputterminal of said low-inertia motor being connected to said groundreference voltage.
 2. The bidirectional amplifier of claim 1 wherein thesupply voltage of said first stage of said current amplifier is notstabilized.